Pin plate arrangement for a piano

ABSTRACT

A pin plate arrangement for a piano comprising a first plurality of bonded together plies of wood, a second plurality of bonded together plies of wood, and intermediate layers of wooden members interposed and bonded between the first and second pluralities of plies, each of the plies of the pluralities of plies being smaller in thickness than each of the intermediate layers, and the individual plies of the pluralities of plies being bonded together with a set resin, whereby a sufficient pin holding force of the pin plate is maintained for a long period of time even with changes in atmospheric conditions.

United States Patent [191 Okugawa [451 Apr. 23, 1974 FIN PLATE ARRANGEMENT FOR A PIANO [75] Inventor: Toshlmune Okugawa, Kasai, Japan A [73] Assignee: Nippon Gakki Seizo Kabushiki Kaisha, I-Iamamatsu-shi, Shi'zuoka-ken, Japan [22] Filed: Feb. 20, 1973 [21] Appl. No.: 333,722

Related US. Application Data [63] Continuation of Ser. No. 110,211, Jan. 27, 1971,

abandoned.

[30] Foreign Application Priority Data 1,212,775 l/l917 Kantor 84/186 WP FOREIGN PATENTS OR APPLICATIONS 526,130 6/1956 Canada 84/186 WP Primary Examiner-Lawrence R. Franklin Attorney, Agent, or Firm-Flynn & Frishauf [57] ABSTRACT A pin plate arrangement for a piano comprising a first plurality of bonded together plies of wood, a second plurality of bonded together plies of wood, and intermediate layers of wooden members interposed and bonded between the first and second piuralities of plies, each of the plies of the pluralitiesof plies being smaller in thickness than each of the intermediate layers, and the individual plies of the piuralities of plies being bonded together with a set resin, whereby asufficient pin holding force of the pin plate is maintained for a long period of time even with changes in atmospheric conditions.

10 Claims, 12 Drawing Figures PATENTEDAPR23 mm 36051666 SHEET 1 BF 4 FIG.

PATENTEDAPR 2 1974 3805x566 SHEU 2 UP 4 PIN PLATE ARRANGEMENT FOR A PIANO This is a continuation of application Ser. No. 1 10,21 I filed Jan. 27, 1971, and now abandoned.

The present invention relates to a pin plate arrangement for a piano and more particularly to improvements in a pin plate arrangement for a piano which conventionally consists of laminae of wooden plates, the grains of which intersect each other substantially at right angles between the adjacent plates.

A piano is generally so designed as to produce a sound of a prescribedtone when selective depression of any of the keys juxtaposed in the order of musical notes causes the corresponding string to be struck by a hammer. The string is supported at one end by hitch pins embedded in a piano frame and at the other end by tuning pins embedded in the undermentioned pin plate (wrest-plank).

In the prior art pianos, there is disposed a pin plate 12, as shown in FIG. 1, on the inside of a piano frame 11 open at the bottom and assuming a channel shape in section. One end portion of the piano frame 11 is bored with through holes 14 at a point facing one end of a string corresponding to each key, the other end of which is supported by the aforesaid hitch pins (not shown). Those parts of the pin plate 12 which face the through holes 14 are perforated with a plurality of pin support holes 15 having a suitably smaller diameter than said through holes 14. Into the pin support holes 15 are inserted under pressure a plurality of tuning pins 16 (hereinafter simply referred to as the pins) through the corresponding through holes 14. Those portions of the pins 16 which project above the surface of the frame 11 support the end of the corresponding string 13. In this case, the outer periphery of that part of each pin 16 inserted into the through hole 14 is covered with ring bush 17.

A pin plate for-a piano having the aforementioned construction should always support the pins 16 with a sufficient strength to allow the string to have a substantially constant tension over a long period of time with a proper degree of compressibility and elasticity.

Heretofore, there has been favorably accepted a wooden pin plate illustrated in FIG. 2 in consideration of various factors such as the aforesaid strength with which the pin plate is desired to support the pins, and the economics and mass production of the plate. Namely, a pin plate according to the prior art consists of laminae .of relatively thick (generally about 5 to 8 mm) wooden plates 21 (commonly hard wooden materialsuch as maple), the grains of which intersect each other substantially at right angles between the adjacent plates. Each wooden plate 21 consists of a plurality of wooden strips 21a, 21b, 21c, connected together side by side.

A pin plate arrangement constructed as described above has compressibility and elasticity equal to about 1/10 of those of plastics materials and about 1/10 of those of metals, so that when the pin is inserted into the support hole 15 under pressure, the inner wall of the hole 15 is suitably deformed due to compression, but immediately after regains an adequate degree of elasticity to be pressed against the outer periphery of the pin 16, thereby supporting it with a sufficient strength.

When the pin is inserted into the support hole 15 and the string is attached to the end of the pin for tension,

the pin is subject not only to a tensional force acting in the direction in which the string is stretched but also to a twisting force in a certain direction when the string is struck, so that the pin plate arrangement should always exert a sufficient frictional force to the pin to maintain it at a prescribed position against the aforementioned external forces.

Since, however, wooden material generally tends to expand or contract due to variations in atmospheric humidity, the conventional pin plate arrangement has the drawback that its force applied in supporting the pin varies with changes in the humidity. For this reason, the prior art piano using a pin plate arrangement shown in FIG. 2 had the disadvantage that during long use, there often occurred disorder in the tone pitches due to displacement of the pin from its proper position.

For instance, when atmospheric humidity decreases, the wooden plate 21 contracts to broaden the diameter of the pin support hole 15. As a result, the frictional force applied by the pin plate arrangement to support the pin is reduced to cause the pin to be so displaced as to slacken the tension of the string. If, under such condition, the key is depressed, the tone derived from the corresponding string will present a disorderly pitch.

Conversely where atmospheric humidity increases, the wooden plate 21 swells to contract the pin support hole 15. While in this case, there seems to be no problem due to the pin plate arrangement applying a greater frictional force to support the pin, the wooden plate 21 presents different degrees of expansion between those parts thereof facing the top and bottom of the pin support hole 15, probably because the plate arrangement is fixed to the piano frame 11 (or permissibly a suitable support rod), as shown in FIG. 1, only along the entire side periphery and at the top. This event often. leads to cracks in the inner wall of the pin support hole 15 to reduce the frictional force of the pin plate arrangement to support the pin as in the preceding case.

Further, the tensional force and twisting torque applied by the string to, the pin inserted into the pin support hole 15 grow larger toward the top and bottom of said hole 15, starting approximately with the vertical center of the pin. Thus the aforesaid cracks tend to appear more concentrately at those parts of the inner wall of the pin support hole 15 facing the top and bottom of the wooden plate 21 than at those parts of said hole 15 facing the vertical center of the pin.

It is, therefore, the object of the invention to "provide a pin plate arrangement for a piano which does not decrease in frictional force to support pins, no matter how atmospheric humidity varies, but is always capable of supporting the pins with a sufficient force to cause the string to be stretched with a substantially constant tension over a long period of time.

SUMMARY OF THE INVENTION According to an aspect of the present invention, there is provided a laminated pin plate arrangement for a piano comprising plural intermediate layers of wooden members, first cross-grain plies of wood, and second cross-grain plies of wood, each of the plies of the pluralities of plies being bonded with a set of resin, and the plural intermediate layers being interposed and bonded between the first and second pluralities of bonded together plies. The thickness of each crossgrain ply of the pluralities of plies being smaller than that of each intermediate layer.

The present invention can be more fully understood from the following detailed description when taken in connection with the accompanying drawings, in which:

FIG. 1 is a fragmentary sectional view of a pin plate arrangement for a piano, showing a fundamental construction in use;

FIG. 2 is a perspective view of the prior art pin plate arrangement for a piano;

FIG. 3 is a perspective view of a pin plate arrangement according to an embodiment of the present invention;

FIG. 4 is a fragmentary sectional view of the pin plate arrangement of FIG. 3 in use;

FIG. 5 is a perspective view of a modification of the pin plate arrangement of the invention;

FIG. 6 is a graphical illustration of comparison between the frictional force of a pin plate arrangement according to the invention to support tuning pins and that of the prior art;

FIG. 7 is a perspective view of a pin plate arrangement for a piano according to another embodiment of the invention;

FIGS. 8A to 8D are schematic illustrations of the preferable overall percentage thicknesses occupied by the laminae of relatively thin plate members in the entire pin plate arrangement of the present invention; and

FIG. 9 is a perspective view of a pin plate arrangement for a piano according to still another embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 3 is a perspective view of a pin plate arrangement for a piano according to an embodiment of the present invention. According to thisembodiment, plural layers 32 of relatively thick wooden. plates consist of, for example, five layers 31a, 31b, 31c, 31d and 31e of wooden material eachabout 4 to mm thick, for example, of maple, the grains of the layersintersecting each other substantially at right angles between the adjacent layers. Each layer 31 consists of a plurality of elongated wooden strips 311, 312, 313, connected together side by side with a thermosetting resin adhesive agent. The wooden strips 31 1, 312, 313, consti-, tuting one layer 31 have grains extending in the same direction.

Further on the upper and under sides of the thick intermediate layers 32 are superposed, as shown in FIG. 3, first and second cross-grain plies 341 and 342 (for example, three to eight plies, respectively), each ply 33 being about 0.3 to 0.85 mm thick, for example, of beech. The grains of the first and second plies 341 and 342, respectively intersect each other substantially at right angles between the adjacent plies. In this case, the respective wooden plates 33 of the first and second cross-grain plies 341 and 342 are dried in advance to 5 to 10 percent moisture content and under this condition thermally bonded together by a hot press using, for example, a thermosetting phenolic resin adhesive. On the other hand the respective wooden plates 31a to 31: of the intermediate layers 32 are dried in advance to about 5 to 7 percent moisture and under this condition bonded together by a hot press by, for example, inserting pre-preg films or sheets 35a, 35b, 35c and 35d uniformly impregnated and coated with, for example, a thermosetting phenolic resin adhesive between the wooden plates 31a to 312. In this case, the first and second cross-grain plies 341 an 342 are similarly bonded to the intermediate layers 32 with such pre-preg films or sheets 35c and 35f inserted between the interfaces thereof. Alternatively, all of the wooden plates of the entire laminate assembly including the intermediate layers 32 and cross-grain plies 341 and 342 may be bonded together at once using the aforesaid thermosetting resin adhesive or pre-preg films impregnated therewith. The wooden plates are first dried and then bonded together. The aforementioned bonding operation was carried out under the following conditions.

When pre-preg films When adhesive agent was were used. applied directly to wooden plates Temp. Time Temp. Time Drying about about about about 30 condiil0C 5min 60tl0C to 70min tion Bonding about about 70 about about 70 condil45iSC to l20min l45i5C to l20min tion One end portion of the pin plate arrangement 36 for a piano manufactured as described above is perforated with a plurality of pin support holes 43 having a slightly smaller diameter than tuning pins 42 for supporting the end of strings 41 so that the pins 42 are inserted into the holes 43 under pressure in the undermentioned manner. The pin plate arrangement is fixed, for example, to the inner wall of a piano frame 44 open at the bottom and assuming a channel shape in section. The upper wall of the frame 44 facing the pin support holes 43 is bored with through holes 45 having a suitably larger diameter than the pins 42. The pins 42 are inserted into the through holes 45, for example, by an air hammer, so as to support the end of the corresponding strings 41 by the end portion of the pins which project above the frame 44. Thereafter the pins 42 are screwed into the pin support holes 43 by being turned several times through the screw grooves 46 formed in the lower half of the pins 42.

As mentioned above, the respective wooden plies or plates 33 of the first and second cross-grain plies 341 and 342 disposed on both sides of the intermediate layers 32 are bonded together by a set thermosetting resin adhesive, so that, as compared with the prior art, the pin plate arrangement of the presentinvention more effectively prevents the thick intermediate layers 32 from being affected by atmospheric humidity, no matter how it varies, due to the presence of the aforesaid large numer of set resin adhesive layers. Since the ex pansion and contraction of the wooden plates 31 of the intermediate layers 32 caused by variations in ambient atmosphere is more reduced than has been possible in the past, the pin plate arrangement of the present invention can supply a substantially constant frictional force to the pins 42, thereby effectively preventing the disorderly tension of the strings 41.

Further, the interfaces 31a to 31f between the respective wooden plates of the intermediate layers 32, as well as between the layers 32 and the first and second plies 341 and 342 may be thermally bonded by using pre-preg films 35a to 35f impregnated with a thermosetting resin adhesive follow-ed by drying. Accordingly, atmospheric moisture does not intrude into the wooden plates 31 of the intermediate layers 32,

permitting the moisture content of the laminate assembly as a whole to be maintained at an extremely low level. This eliminates the necessity of conducting drying for many hours as has been required for the prior art pin plate arrangement and in consequence providing such drying equipment, thereby reducing manufacturing cost.

When pressed under heat, the thermosetting resin adhesive coated on the films 35a to 35f pass into the wooden plates 31 of the intermediate layers 32 to reinforce their fibrous tissue, and their grains intersect each other substantially at right angles between the adjacent plates, prominently minimizing the occurrence of cracks around the pin support holes 43 as has often been observed in the past.

What should be noted at this point is that the first and second cross-grain plies 341 and 342 are not additionally mounted on the conventional thick intermediate layers 32, but part of the intermediate layers 32 is simply converted to such cross-grain plies, so that manufacturing cost does not rise higher than in the past, but rather permits inexpensive production.

FIG. 5 shows a modification of the pin plate arrangement 361 of the present invention where the intermediate layers 32 consist of three wooden plates or layers 31a, 31b and 310 instead of five in FIG. 3. It will be apparent that such pin plate arrangement has the same effect as that of FIG. 3.

Now it may be contemplated to form the entire pin plate arrangement only of such thin hard wooden plates as constitute the aforesaid cross-grain plies 341 and 342. In such case, however, the interfaces between the laminated thin wooden plates are filled with the aforesaid thermosetting resin adhesive, presenting an extremely rigid structure, so that when the tuning pins are inserted into the pin support holes, there is less allowance for such rigid pin plate arrangement to display sufficient compressibility and elasticity with respect to the tuning pins. This further leads to loss of the favorable characteristics of wooden material and strict dimensional precision demanded of the pins and pin support holes and most likely variation in the frictional force applied by the rigid pin plate arrangement to the respective pins. For this reason, the aforementioned pin plate arrangement is undesirable from the standpoint of practical use.

FIG. 6 is a graphical illustration of comparison between the frictional force of a pin plate arrangement according to the present invention and that of the prior art. The curve 51 of FIG. 6 denotes the property of the pin plate arrangement 36 or 361 of the present invention constructed as shown in FIG. 3 or 5 (the wooden plates of the intermediate layers have been set about 6 mm thick, and each of the first and second cross-grain plies is 4 mm thick, and each cross-grain ply is 0.75 i 0.5 mm thick), and the curve 52 shows the property of the prior art pin plate arrangement constructed as shown in FIG. 2 (consisting of five wooden layers each about 6 mm thick and one wooden plate about 8 mm thick). As is apparent from FIG. 6, the pin plate arrangement of the present invention not only has a greater frictional force with respect to the tuning pins than the prior art, but also presents a smaller attenuation or decrease in said frictional force after drying is conducted for a prescribed number of days (For example, after 100 day drying, the pin plate arrangment of the present invention has only showed an about 29 percent attenuation or decrease of said frictional force, whereas the conventional type has indicated an attenuation of as large as percent). The curve 53 of FIG. 6 represents the property of another prior art pin plate arrangement consisting of only a lamination of the aforesaid thin hard wooden plates (25 plates each about 1.5 mm). As compared with this arrangement, the present invention will be understood to be far more excellent. This experiment was made at a temperature of about 35C and a relative humidity of about 20 percent.

FIG. 7 illustrates another embodiment of the present invention where there are disposed cross-grain plies not only on the upper and under sides of the intermediate layers 32 but also in the central part thereof. That is, cross-grain plies 343 are interposed between the wooden layers or plates 31b and 310 of the intermediate layers 32. The respective plates of the plies 343 are adhered together by the use of a thermosetting resin adhesive or pre-preg sheets thereof as in the case of the above-describedcross-grain plies 341 or 342. It will be apparent that such construction will have the same effeet as that of FIG. 3 or 5.

In the above-mentioned cases, it has been found most effective that, when the pin plate arrangement consists of the first and second cross-grain plies and intermediate layers as shown in FIGS. 8A and 8B, the overall thickness of the first and second cross-grain plies 341 and 342 accounts for 13 to 55 per cent of that of the entire pin plate arrangement, the remainder being constituted by the intermediate layers 32 and that, when the pin plate arrangement consists of the first, second and third cross-grain plies and intermediate layers as shown in FIGS. 8C and 8D, the overall thickness of the cross-grain plies accounts for 20 to 55 per cent of that of the entire pin plate arrangement. Exemplary dimensional relations therebetween are described in FIGS. 8A to 8D.

It will be noted that the thickness of the pin plate arrangement is beforehand made larger than that described in FIG. 8 by several millimeters and is thereafter adjusted by having its upper and/or under side planed off, before it is aligned with the piano frame which is generally made of cast metal with a relatively loose dimensional precision. However, where the upper and lower portions of the pin plate arrangement are formed of thin plies 341 and 342 consisting of a plurality of thin hard wooden plates 33 each 0.3 to 0.85 mm thick, a cutting blade is likely to slip on thethermosetting resin adhesive layer interposed between said wooden plates 33, presenting difficulties in planing off the surface.

FIG. 9 illustrates another embodiment of the present invention adapted for such case. On the surfaces of the first and second plies 341 and 342 there are laminated hard wooden plates 61 and 62 about 2 to 3 mm thick respectively which are of beech or maple. This construction has the advantage that the overall thickness of a pin plate arrangement can be adjusted simply by planing off either or both surfaces of said wooden plates 61 and/or 62 in order to be properly mounted on the piano frame.

All the foregoing embodiments relate to the case where the grains of the wooden plates 31 of the intermediate layers intersected each other substantially at right angles. However, such intersection has only to be realized at least in one plane. Namely, even if there are used intermediate layers wherein the grains of adjacent wooden plates are parallel to each other and those of the immediately upper and lower wooden plates intersect those of the former, then'the present invention can obviously be practised with the same result.

What is claimed is:

l. A laminated pin plate arrangement for a piano comprising:

a plurality of intermediate layers of wooden material, each intermediate layer being about 4 to mm thick; 7

a first plurality of cross-grain plies of wooden material bonded together with a set resin;

a second plurality of cross-grain plies of wooden material bonded together with a set resin;

each ply of said first and second pluralities of plies being about 0.3 to 0.85 mm thick; and

said plurality of intermediate layers being interposed and bonded between said first and second pluralities of plies to form a laminated assembly, said first and second pluralities of plies accounting in terms of thickness for about 13 to 55 percent of the entire pin plate assembly thickness including the intermediate layers.

2. A pin plate arrangement as claimed in claim 1 comprising an odd number of said intermediate layers.

3. A pin plate arrangement as claimed in claim 1 including a third plurality of cross-grain plies of wooden material bonded together with a set resin, said bonded together third plies being interposed in the intermediate part of said intermediate layers.

4. A pin plate arrangement as claimed in claim 3 wherein said first, second and third pluralities of plies account in terms of thickness for about 13 to 55 percent of the entire pin plate assembly thickness including the intermediate layers.

5. A pin plate arrangement as claimed in claim 3 wherein said intermediate layers are formed of maple wood and said pluralities of plies are formed of beech wood.

6. A pin plate arrangement as claimed in claim 1 including at least one separate wooden plate mounted on the outer surface of at least one of said first and second pluralities of plies, whereby the outer surface of said at least one plate is planed off for adjustment of the overall thickness of the entire laminate assembly.

7. A pin plate arrangement as claimed in claim 1 wherein said intermediate layers are formed of maple wood and said pluralities of plies are formed of beech wood.

8. A pin plate arrangement as claimed in claim 1 wherein said set resin used as a bonding agent is a thermosetting type resin.

9. A pin plate arrangement as claimed in claim 8 wherein said bonding agent is a pre-preg film or sheet impregnated with said thermosetting type resin.

10. A pin plate arrangement as claimed in claim 1 wherein said intermediate layers are cross-grain layers. 

1. A laminated pin plate arrangement for a piano comprising: a plurality of intermediate layers of wooden material, each intermediate layer being about 4 to 15 mm thick; a first plurality of cross-grain plies of wooden material bonded together with a set resin; a second plurality of cross-grain plies of wooden material bonded together with a set resin; each ply of said first and second pluralities of plies being about 0.3 to 0.85 mm thick; and said plurality of intermediate layers being interposed and bonded between said first and second pluralities of plies to form a laminated assembly, said first and second pluralities of plies accounting in terms of thickness for about 13 to 55 percent of the entire pin plate assembly thickness including the intermediate layers.
 2. A pin plate arrangement as claimed in claim 1 comprising an odd number of said intermediate layers.
 3. A pin plate arrangement as claimed in claim 1 including a third plurality of cross-grain plies of wooden material bonded together with a set resin, said bonded together third plies being interposed in the intermediate part of said intermediate layers.
 4. A pin plate arrangement as claimed in claim 3 wherein said first, second and third pluralities of plies account in terms of thickness for about 13 to 55 percent of the entire pin plate assembly thickness including the intermediate layers.
 5. A pin plate arrangement as claimed in claim 3 wherein said intermediate layers are formed of maple wood and said pluralities of plies are formed of beech wood.
 6. A pin plate arrangement as claimed in claim 1 including at least one separate wooden plate mounted on the outer suRface of at least one of said first and second pluralities of plies, whereby the outer surface of said at least one plate is planed off for adjustment of the overall thickness of the entire laminate assembly.
 7. A pin plate arrangement as claimed in claim 1 wherein said intermediate layers are formed of maple wood and said pluralities of plies are formed of beech wood.
 8. A pin plate arrangement as claimed in claim 1 wherein said set resin used as a bonding agent is a thermosetting type resin.
 9. A pin plate arrangement as claimed in claim 8 wherein said bonding agent is a pre-preg film or sheet impregnated with said thermosetting type resin.
 10. A pin plate arrangement as claimed in claim 1 wherein said intermediate layers are cross-grain layers. 